1. Field of the Invention
This invention relates to N,N'-hydrocarbylenebis[N-(2,2,6,6-tetraalkyl-4-piperidinyl)amic acid hydrazides] and their derivatives. These compounds are useful for stabilizing polymeric systems which are subject to degradation and/or discoloration upon exposure to heat and/or light. These compounds contain at least two hindered amine light stabilizing groups (HALS groups) and two hydrazide (or hydrazide derivative) thermal oxidative stabilizing groups.
The amic acid hydrazide functionality in these compounds enhances the photooxidative stabilizing properties of the hindered amine groups and contributes thermooxidative stabilizing and metal complexing properties to the compounds.
The non-derivatized bis hydrazide precursors are reactive stabilizers that can be attached to compounds containing anhydride or carboxylic acid groups. Due to the reactive bis hydrazide groups they can be incorporated into polyesters, polyamides, polyimides or combinations thereof, during the polymerization step to form permanently bound stabilizing groups.
The novel derivatives of the hydrazides have low volatility and are not readily lost from polymeric systems via volatilization, migration or extraction.
2. Description of the Prior Art
It is well known in the art to use hindered amine compounds to retard the deleterious effect of ultraviolet radiation on synthetic polymers. Hydrazides and hydrazide derivatives are used commercially for stabilizing polyolefins. (See Encyclopedia of Polymer Science and Engineering, 2nd Ed. Vol. 2, pp. 83-84 (1985)). However, there are only four examples in the literature where the hindered amine moiety and the hydrazide moiety (--R--C(.dbd.O)--NH--NH.sub.2, where R is not O, N or S) are present in the same molecule. None of these examples have more than one hindered amine moiety in the molecule. None of these prior art compounds are hydrazides of amic acids.
Previously known HALS hydrazides are: ##STR1##
U S. Pat. Nos. 4,145,512 and 4,178,279 teach reacting hindered amine light stabilizers containing carboxylic acid hydrazide groups with isocyanate groups of polyisocyanates or isocyanate prepolymers to obtain light stabilized polyurethanes. However, the HALS-hydrazides employed were of the prior-art type. They did not have the amic acid hydrazide structure which enhances the light stabilizing properties of our novel compounds.
Although they are not "prior art," copending U.S. Pat. application Ser. No. 310,408, filed Feb. 13, 1989, and abandoned parent U.S. Pat. application Ser. No. 84,602, filed Aug. 12, 1987, both assigned to the assignee of the present invention and application, disclose N-(2,2,6,6-tetraalkyl-4-piperidinyl)amic acid hydrazides having the general formula: ##STR2## These amic acid hydrazides are efficient light stabilizers, the hydrazide group providing a means of attaching the light stabilizer to anhydride containing copolymers.
U.S. Pat. No. 4,857,595, assigned to the assignee of the present invention and application, discloses HALS hydrazides attached to maleic anhydride copolymers.
U.S. Pat. No. 4,857,596, also assigned to the assignee of the present invention and application, discloses polyfunctional polymers or copolymers in which HALS hydrazides and UV absorbers or antioxidants are attached to anhydride containing polymers or copolymers.
All of the prior art hydrazides substituted with hindered amine light stabilizing groups are of relatively low molecular weight. Appreciable amounts of these stabilizers may be lost due to volatilization during processing when incorporated into polyolefins or engineering thermoplastics. None of the prior art hydrazides fall under general structure I of the present invention. None of the prior art hydrazides contain more than one reactive hydrazide group in the structure.
In addition, the prior art HALS hydrazides may only be attached to polyurethanes, polyesters, polycarbonates, polyamides or polyimides as end-capping groups. The prior art HALS hydrazides cannot be incorporated into the backbone of the polymers.